Manufacture of electric detonators



Oct. 5, 1943. w. TAYLOR ETAL MANUFACTURE OF ELECTRIC 'ma'rouuons Filed Fb. as. 1940 FIG. 4

INVENTURS Wilfrid Tag Maldwgri. .lunes EB a. W A ATTORNEY FIG. I

;Pnented On. 5, 1943 a tuner-norms or Emcrmc nE'roNA'roas Wilfrid Taylor, Saltcoats, Scotland, and Maldwyn' Jones, Manchester, England, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application February 28, 1940, Serial No. 321,301 In Great Britain March a, 1939- Claims.

known to efiect the-sealing by crimping the metal detonator tube onto a vulcanised' indiarubber plug through which the electric conductors pass into, the interior of the detonator.

Vulcanised indiarubber does not become appreciably plastic when it is exposed to warm temperatures or relatively high pressures such as are experienced in storage. or in blasting Practice, but retains its outstandingresilient properties under these conditions. As long as the material of the plugis in good condition it therefore maintains a continuous pressure against the conductors and the wall of the detonator tube into which it is crimped. So longas the indiarubber remains in good condition, vulcanised indiarub ber plug detonators are thus remarkably free from, the type of failure due to the entry of water orvmoisture. Vulcanised indiarubber, however, as is well known, sooner or later perishes and becomes brittle;- andunder warm storage conditions the life of the vulcanised indiarubber plug electric detonator is somewhat shorter than is generally considered desirable for electric detonjators. For some applications of electric detonators, moreover, especially blasting in' fiery mines, it. is desirable that-the sealing material employed should be of low inflammability, and

preferably less inflammable than rubber.

Although many materials are 'known which either have better. storage properties or are less inflammable than indiarubber, it has hitherto been impossible to produce crimped plug electric detonators capable under service conditions of resisting the entry of water into the interior as eflectively by the use of compositions free from indiarubber as by the use of compositions containing indiarubber.

We have now found that by crimping the charged 'detonatortube over a plug of resilient material based on vul-cansed polymerised 2- chloro-butadiene 153 (a material known as neoprene) through which the twisted insulated electric conductors extend'towards the electric initiating element to which they are attached, we can produce an electric detonator which can not only be stored without deterioration for much longer periods under good or even bad storage condirtions than vulcanised indiarubberplug electric detonators, but which can also adequately resist the entry oiflwater undera wide range of pressure conditions; even after prolonged exthe manufacture of electric detonators, it is the formation of traces of the dangerously sensitive cooper aside in presence of tracesof moisture. The neoprene compositions are also less inflammable than vulcanised inciiarubber.

In' putting the invention into effect, we may employ the neoprene compounded with other in- I In the case of detonators intendedto be used in fiery, or gassy situations, the comgradients.

pounding ingredients of the neoprene composition may include organic ingredients of namequenching, non-inflammable or but slightly in flammable character, for instance, waxy chlorinated hydrocarbons. The'insulated covering of the'electric conductors leadingto the electricinitiating element of the detonator is left intact at the position occupied by the neoprenecomposition plug. 4 According-t0 one form of the invention the neoprene composition is extruded into the form of aperiorated tube before vulcanisation is carried out or completed and the plugs are ia sh-.

ioned by cutting theextruded tubes into lengths and threading the insulated conductors through the vulcanised tubes. It is convenient to vulcanise the tubes before cutting them.

According to another form of the invention the neoprene composition in its still thermoplastic unvulcanised oronly partly vulcanised condition is first moulded underpressure at raised temperature around the axially disposed insulated and twisted conductors into a form having a cylindrical surface and is vulcanised thereafter to form structures in which the insulated and twisted leading wires are "firmly embedded in plugs of vulcanised neoprene composition.

In the drawing attached hereto, Fig. 1 is a I longitudinal'section of a charged detonator in plug of neo'prene composition through which the posur'e to warm storage. We may therefore employ which a tubular neoprene composition plug, bearing the insulated conductors to the stripped ends of which a iuzeheadhas been attached, is positioned readyior crimping; Fig.2 represents a longitudinal section of the detonator after the plug has been crimped, and Figs. 3 and 4 repre..

sent respectively a side view and plan of the crimped end of the detonator. Inlthe drawing I represents the detonator tube containing an initiating charge 2. 3 represents a cylindrical insulated portions 4 and 5 of; the electric conductors pass. The stripped ends 6 and 'l of these conductors are attached to the poles 8 and 9 of the fuzehead II) by spots of solder II and I2. The resin-wax coating II on the insulated conductors 4 and 6 extends slightly above-the top of the plug. In Fig. 2, the general reduction in diamand the corresponding extension in length of the neoprene composition plug are shown.

i i Since according to the present invention the waterproofing effect depends on the emcient compression by the crimp or the resilient plug eter of the crimped portion of the 'detonator tube severance'ot the leading'wires between the adiace'nt plug's arid the removal or the insulation from their extremities, ii! required, and the attachment oi the primary i electrical ignition means, e. g. the bridge wires or i'uzeheads, may

- be carried out in any suitable succession of steps after the plugs have :been moulded about the leading wires, due regard being paid to the nature or any vulcanisation treatment required; and the against the wall of the detonator tube and 1 against the conductors passing through it, an efficient type of crimp isnecessary. V

A crimping apparatus especially suitabl for the manufacture of electric detonators according to the present invention first grooves the tube longitudinally around the plug to form a quatre toil section, then flattens the lobes or the quatreioil radially to iorm a' substantially cylindrical neck of reduced radius on the tube;- the superfluone metal being iorced intoa flattened sigmoid told at each side of each groove. I The electric, initiating element may convenientlytake the tom of an electric "iuzeheadoi the kind'in which the initiating composition isva coherent bead.

It has been proposed to iform, a orimped plug 7 electric detonator in which a vulcanisablethermopias'tic composition having resilient properties manner that the extremities oi the insulationare enclosed in the plug, and the bare portions 01' the 7 wire protrude through the extension. According,

to this proposal the vulcanisable composition may be' vulcanised during the moulding opera- The present invention, however, presents the advantage that theinsulation or thedetonator leading wires may be continued Beyond the plug into the body 01 the detonator, thereby minimiz- "ing the risk of stray current the attachment or a'ready-mads tusehead;

' and also that it facilitates the stripping of the .ends of the insulated wires.

According to that form 0! the invention in which the vulcanised plug is threaded ontothe insulated conductors the twisting may be carried v s The invention isfurther illustrate ignition and allow Mogiieeium time out before or during the twisting operation. Ac-

cording to form oi-the invention in which, the-plus is Oulded about the twisted and insulated wires the mouldingoperation mayconveng iently b6 carried out in amultiple unit mould to :produce ,at each operation a number of plugs in which twisted leading wires are' embedded; 'rne lnsiusieii leading wires may be already out and twisted, and i1- deslred also the inculation may beaiready stripped from their ends,

f or the twistedwires may be'in the form of a continuous length 'passingthrough each unit or the mould. The plugs moulded roundthejwisted insaluted wires may be removed from the moulds as soonas theyhave set sumci'ently to retaintheirand theivulcanisation-is thereafter accomon the vulcanisation loaded detonator 'tubes are finally crimped around the lugs carrying'the leading wires to. which the primary ignition means have been atn The mould may conveniently be made in two portions each containing a number of. cavities cooperating. to define cylindrical unit cavities at intervals around suitably guided axially situated twisted insulatedleading wires, suitable means being provided whereby the twisted leading wires may be distanced as desired betweenadjacent cavities, so that a continuous length or wire may be employed. But if twistedlengths of insulated leading wires previously cut to;a desired length are used, the distancing means may be omitted.

.' The mould is provided with arrangements whereby the cavities can be heated, and if desired also it may be provided with means whereby they can be Jchilled. The neoprene composition may be introduced into the cavities in t e form of strips, lumps or the like'in such-quan ty that when'the mouldis closed and pressure i applied the composition will beioroied into intimate contact with the twisted leading wires running axially through the..cavities, and provide an, expess over what is required to complete e cylinder. Provision may be made for the surplus to nowvaxially or in some other convenient direction to form a Alternatively, if desired, an iniection type or moulding apparatus may be employed, but in this case tlre'neoprene composition employed must be such-that it will not set during the period for whichit is'present in the apparatus;

a by the following example in which the parts are parts by weight: a i v 7 Examplel i o I Parts Neoprene i f 10 Wood rosin a 5 Zinc oxide 1i) Nonox 8 (registered trade-mark) 2 Polychlor-naphthalene (melting 68 C.) .s.. 5 .55 Cotton-seed o 5.

'Vulcanised rape-seed -oil.-. 20, Whiting Titanium dinzidn 10 VulcaforYellow G. S-f '3 ,Theabove ingredients are extruded under presto 5.5 mm. and the central orifice about 15 to 2.0 mm. The tubing-is yulcanised by heating it in an autoc of about 8 mm. The leading wires, already pro- Q (vide'd with "a suitable insulation arid-twisted)- completed by stovirig. storage or other.

gether, then through the central hole indzhe plug. with thegaid oi a littletalc, and

lave c1 40. lb. steam pressure about f tlisruzelieeuisattecheutothsbsrod ends-'0! these wires. The iuzehead and leading wires are waxed in a resin-wax bath at about 130 C. for a suitable distance. and the plug is then slipped over the waxed wires while the wax is still fluid, and adjusted to its proper position against the fuzehead. The plug is then inserted to a suitable depth into the end of a No. 6 fulminate-chlorate copper detonator oiwhich the diameter at the mouth'is approximately 5.97 mm. and crimped mechanically with multiple crimps so as to pinch the walls of the detonator deeply into the plug and make a tight Joint also with the crimped leading wires. The detcnator of this example can be used in fiery mines. It can also be used for submarine blasting.

Example 2 Quantities of the composition used according to Example 1, each more than sufilcient to form the cylinder, are introduced into the cavities of one plate of a mould of the separable type in which the twisted insulated leading wires have been positioned. The mould cavities are shaped so as to permit surplus material to escape axially at one end to form a flash when the other plate of the mould is pressed home. The temperature of the mould is approximately 160 C. and the mould remains closed under pressure for one minute. It is then opened and the twisted leading wires with their adhering plugs, which have been set in shape by their incipient vulcanisation, are withdrawn. The plugs with the leading wires are then placed in a stove and heated by means of live steam at 40 lb. pressure at approximately 140 C. for one hour, by which time they are setisfactorily vulcanised. The diameter of the cylindrical portion of the plugs including the wires is such as to permit of their being just entered without difllculty into a No. 6 detonator tube. The depth of the cylindrical portion or the plug is about 8 mm. The wires are cut at a distance of about from the end of each plug opposite to the flash. The insulation is stripped from the greater part of the short end of the wires and also from the remote ends of the wires. The flash is trimmed. Fuzeheads are then soldered on to the short bared ends and charged No. 6 detonator tubes are crimped around the plugs by means of a Briese crimp.

Having now particularly described and ascertained the nature of our said invention, and in what manner the same is to be performed, we declare that what we claim is:

1. An electric detonator in which the insulated electric conductors leading to the electric initiating element are twisted together and pass through a resilient electric plug comprising vulcanised polymerised 2-chloro-butadiene-1:3 crimped into the mouth of the charged detonator tube.

2. A detonator as claimed in claim 1 in which the initiating element is in the form of a head bead.

3. A detonator as claimed in claim 1 in which the 2-chloro-butadiene-l:3 composition contains organic ingredients of a flame-quenching, noninflammable character.

4. A process for sealing an electric detonator, which process comprises positioning about the insulated and twisted electric conductors a sealing plug of resilient material comprising vulcanised polymerised 2-chlorobutadiene-1:3, attaching the electric initiating element, and crimping the plug with the conductors and initiating element in position into the mouth 01. the charged detonator tube.

5. A process as claimed in claim 4 in which a tubular plug of vulcanised 2-chloro-butadiene- 1:3 is first formed and then threaded on to the insulated conductors.

6. A process as claimed in claim 5 in which the 2-chloro-butadiene-lz3 composition is extruded into the form of a tube and is subsequently vulcanised and cut into lengths.

7. A process as claimed in claim 4 in which the plug is moulded about the twisted insulated conductcrs.

8. A process as claimed in claim 7 in which the vulcanlsation oi the 2-chloro-butadiene-1:3 composition is carried out after it has been moulded about the twisted wires.

9. A process as claimed in claim 4 in which the ends of the conductors protruding through the plug are stripped and trimmed after positioning the sealing plug on the conductors.

10. A detonator as claimed in claim 1 wherein the tube is crimped to the resilient plug by grooving said tube to form a quatreioil section flatttening the lobes of said quatreioil radially to form a substantially cylindrical neck of reduced radius and forcing the superfluous metal into a flattened sigmoid told at each side of each groove.

WILFRD) TAYLOR. MALDWYN JONES.

v CERTIFICATE OF 'cohnscnon, Potent No. 25514007. October 5,,1943.

WIIFRED TAYLOR, ET AL.

or the above numbered patent ieqpizing correction ea follows: Page 3, second column, line 10', strike out the word 'head"; -l1ne 29;. for f'claim 5" J ead --cla1m line 36, for "91:12:17": read --o la1 m l and that the It is hereby certified thaterror-a apeare .inthe printed specific tion said Letters Patent shoxild be 'reid with 1mm come'uo enema; that the sam ay xirorm t to om-d of'the oaeel'in' the Patent. 10m,-

Signed and u'alea tml 25rd day or Novemb r, ,-'p.. 1945;

Henry ven Arsdale, (Seal) Acting Commissioner of Patents.

cnanrxcnzor comm-Ion, Petent Ho. 2,5}13007. I October 5,,1945.

WILFRED mmon, ET AL.

It is hereby certified that'error appears in the printed specification or the above numbered patent requiring correction as rollowa: 'Page 5, second column, line 10, strike out the word 'head"; line 29-, for 'fcleim 5" read --c1a1m 1;"; line 56, to? aid-71mm --e le.1.m h"; and that the and Letters Patent snmild be run with an; correction therein that the some may ooritorm to reord or'the cae e 'inthe Patent Off-ice.

Signed and aenledthie 23rd day or November, 1,). 19143.

Henry Van Aradale, (Sell) Acting Commieeioner of Patents. 

